This invention relates to industrial baghouses and, more particularly, to a tensioning device for connecting cylindrical bag filters to an overhead support.
Continuous emphasis on environmental quality has resulted in increasingly strenuous regulatory controls on industrial emissions. One technique which has proven highly effective in controlling air pollution has been separation of undesirable particulate matter from a gas stream by fabric filtration. Such filtration is carried out in dust collection apparatus known in the trade as a "baghouse" which operates on the same general principle as an ordinary household vacuum cleaner, except on a much larger scale. Basically, the baghouse is a sheet metal housing divided into two chambers, referred to as plenums, by a tube sheet. Disposed within openings in the tube sheet are fabric filters. A particulate laden gas stream induced by the action of a fan, blows into one chamber (dirty air plenum) wherein dust accumulates on the fabric filter as the gas passes through the fabric into the other plenum (clean air plenum) and out an exhaust. Although all baghouses are designed in accordance with the foregoing general principles, there are numerous operational and structural distinctions. The present invention relates to a baghouse wherein a plurality of cylindrical filter bags having closed upper ends are vertically suspended in the clean air plenum from a bag support framework. The lower ends of the bags are fixed to openings in a tube sheet or cell plate. Filtration of the process gas occurs from inside to outside of the bags (i.e., the dust collects on the inside surface of each bag). As a result, baghouses constructed in this manner are normally referred to as inside to outside bag collectors.
During continuous operation of the baghouse the bags must be periodically cleaned to remove the dust cake which accumulates within each filter sleeve. This may be done by interrupting the flow of the process gas carrying particulate matter and then causing reverse cleaning air to flow from the clean air plenum to the dirty air plenum. The reverse flow of cleaning air causes the dust cake to be dislodged and fall through the interior of the bag to the dirty air plenum for removal by an auger or similar means. In some baghouse installations, reverse air cleaning may also be supplemented with mechanical shaking of the filters.
The air cleaning process reverses the pressure drop the fabric filter normally experiences during filtering operation. In other words, the filter sleeve tends to collapse inwardly when being cleaned. This tendency is limited somewhat by circular support rings sewn to the outside of the bag at spaced intervals along its length.
Proper tensioning of the bags plays an important role in eliminating fabric collapse during the cleaning and filtering process. If the bags are stretched too tightly between the support framework and the cell plate, the bags do not collapse during cleaning, but they tend to wear out quickly. If, on the other hand, the bags are installed too loosely then the fabric between adjacent skeletal support rings collapses during cleaning and will not permit the dust cake to fall through the bag to the bottom of the dirty air plenum.
Even when a filter bag is properly installed and tensioned correctly, it is reasonable to expect the fabric to stretch with age and with repeated cyclings between the filtering and cleaning modes of operation. Thus, the bags must be periodically checked and the tension readjusted for each bag from time to time.
The installation and maintenance of filter bags of this genre has traditionally been a time consuming and costly operation. Accordingly, there has been a long felt need in this industry for improvements in filter bag assemblies and mounting techniques to alleviate the many installation and maintenance difficulties which have been encountered.
An earlier solution for properly tensioning filter bags is found in U.S. Pat. No. 4,364,758 of Clements at al issued Dec. 21, 1982 and entitled "Self Tensioning Cap for Bag Filters". This patent is incorporated herein by reference and is generally illustrative of the environment of the instant invention. In cited U.S. Pat. No. 4,364,758, the tensioning feature requires a rigid closure cap which closes the upper end of the fabric filter. Interiorly of the filter bag (i.e., below the cap itself) a tensioning spring is carried on a support rod. When the support rod is mounted on the bag support framework, the tensioning spring acts against the cap and pushes it upwardly relative to the end of the support rod to thus tension the bag. Adjustment may be achieved by supporting the retainer rod through one of a plurality of holes in the support rod by means of a removable pin which acts against the upper surface of the support framework. It is also contemplated in this earlier patent that the tensioning spring can be compressed between the closure cap and the support rod and captured by means of a removable pin. Thus, after installation, the capture pin may be removed to permit the spring to act on the cap and tension the bag.
Application of the foregoing prior art technique is limited, however, to specific baghouse configurations provided sufficient overhead room above the bag support framework to permit both the initial installation and subsequent adjustment of the tensioning assembly. Further, this earlier arrangement placed the flexing components of the tensioning device on the process gas side of the filtering operation which, in some process applications, subjected the flexing members to a rather corrosive environment.
Accordingly, a need remains in the industry for a broad application tensioning device to be employed in a greater range of baghouse configurations. The primary goal of this invention is to fulfill this need.
More specifically, a goal of the invention is to provide a filter bag tensioning device universally adaptable to various baghouse configurations without the need of structural changes within the baghouse.
Another object of the invention is to provide a tensioning device achieving the advantages of accurately pretensioning the filter bags for installation in baghouses having highly limited access above the bag support framework.
An additional object of the invention is to provide a tensioning device of the character described and adapted to baghouse installations wherein limited distance is available between the end of the filter bag and the bag support framework.
Yet another object of the invention is to provide a tensioning device of the character described which may be utilized with filter sleeves having a wide range of end closure configurations.
A further object is to provide a tensioning device which will function with a broad range of configurations of the overhead framework within the baghouse.
Other and further objects of the invention, together with the features of novelty appurtenant thereto, will appear in the couse of the following description.